Prop question on a 20'

[Sceptre20]

I have a 20' Sceptre that is powered by a Yamaha f100 four stroke.I am running a four blade prop on it and find that the boat is unresponsive at slow speeds,it requires constant adjustments at the helm to stay on course and when docking or loading onto the trailer it is very slow to respond,the steering is a brand new baystar hydraulic unit and seems very tight.I was wondering if the four bladed prop could have anything to do with the problem and if others had experienced the same problem.any input would be helpful.

[McGillicuddy]

What prop? What is its pitch? and how are your overall performance numbers? Are your controls Yamaha and dialed in? Seems that tighter steering and a 4 blade would improve response at slow speeds unless way over-propped

[Sceptre20]

It is a Solas amita 17p 4 blade prop.At wide open throttle I get 36mph at 5500-5600 rpm,cruises at 27mph 4600rpm.The recommended range for this engine is 5000-6000 rpm.Thankyou

[Bushwacker]

Originally Posted by Sceptre20

I have a 20' Sceptre that is powered by a Yamaha f100 four stroke.I am running a four blade prop on it and find that the boat is unresponsive at slow speeds,it requires constant adjustments at the helm to stay on course and when docking or loading onto the trailer it is very slow to respond,the steering is a brand new baystar hydraulic unit and seems very tight.I was wondering if the four bladed prop could have anything to do with the problem and if others had experienced the same problem.any input would be helpful.

Sounds like you're simply talking about a slow steering ratio. The prop has nothing to do with that, and Gillie's right, if anything a 4B prop will improve response.

I'm not familiar with Baystar, but I think it's just a cheaper version of the Seastar system, which has 3 different size (displacement) helm pumps. If you have the small size pump, it'll take about 5 1/2 turns of the wheel to move a Seastar hydraulic cylinder lock to lock, and that's pretty slow, especially if you were used to a push-pull cable system, which is typically around 3-3.5 turns. I went with the medium size helm pump, and mine is about 4.5 turns for full stroke of the cylinder, which is still pretty slow but it turns real easy. I'd suggest you disconnect hydraulic cylinder from tiller bar on motor and try turning motor by hand to make sure the bearings in steering shaft aren't dry or binding. Also check the hydraulic lines to make sure a line isn't pinched somewhere, because that would restrict flow and make the helm hard to turn. Those hydraulic helms normally are very easy to turn.

Low speed wander and slow steering response is normal behavior for all planing hulls at low speed, although the "multiple keels" of the VDH makes a SeaCraft track better than most; it just takes some getting used to. You may be over correcting due to the slow response; if you just turn the wheel a small amount and then wait for it to respond, you may find it easier to hold a steady course. Trimming the motor down will also improve steering response.

[FishStretcher]

Originally Posted by Sceptre20

It is a Solas amita 17p 4 blade prop.At wide open throttle I get 36mph at 5500-5600 rpm,cruises at 27mph 4600rpm.The recommended range for this engine is 5000-6000 rpm.Thankyou

I used to run that prop on my 20 MA. Now I run the 15" pitch version since July 2012. WAY Better holeshot and a smidge faster. I keep the 17 as a spare. Sounds like your F100 is stronger than mine, or the boat has better trim. I only pull 34MPH at 6000, or 55-5600, with the 15" or 17" pitch prop. (and the draggy HydroShield)

Fr. Frank called the F100 the YamaDog. He was right. It has no low end torque, so the 15" pitch prop is a lot nicer. It doesn't bog like it did with the 17"

But it sounds like you have a steering issue?

[Sceptre20]

Thanks for the responses,i'll check the sterring pump and hoses

[McGillicuddy]

I think the smaller blades and flex of the aluminum amita 4 might have some impact on slow mo response. But Denny's point about multiple turns and over-correcting on hydraulic steering have much merit. If I could spend your money I'd steer you to a 15p stainless, like say the titan 4 if your a Solas fan. Bigger blade easier to turn and more propulsion at low rpm. Definitely follow up on Denny's suggestions. Your system should respond to a pinky finger... Good luck. Sceptre 20.

[Sceptre20]

Thanks to all